Location and General Description
This ecoregion is located in the northern part of Kenya and extreme southwestern Ethiopia. It encompasses most of Lake Turkana and the Omo River Delta, and grades into the savanna woodlands of the Northern Acacia-Commiphora Bushland and Thicket ecoregion to the west and the Somali Acacia-Commiphora Bushland and Thicket to the east. Mostly lying between 200 and 700 m elevation and gently undulating, it includes the Chalbi Desert, a large flat depression between 435 m and 500 m formed from the bed of an ancient lake.
The climate is hot and dry over most of the year, with mean maximum temperatures of around 30° C and mean minimum temperatures between 18° C and 21° C. There is a short wet season between March and June as the Intercontinental Convergence Zone moves north. Mean annual rainfall is between 200 and 400 mm. Geologically, the ecoregion is located on an outlier of the Tertiary volcanic materials that make up the Ethiopian massif. The soils of the area are complex, and vary from bare rocks and lithosols, with solonchaks, yermosols, and regosols indicating the general desiccation of the area.
Phytogeographically, the ecoregion is part of the Somali-Masai regional center of endemism (White 1983). The vegetation is mapped as ‘Somali-Masai semi-desert grassland and shrubland’ (White 1983). In years of high rainfall, huge areas of semi-desert annual grasslands are found. Aristida adcensionis and A. mutabilis dominate, but during droughts these species and the grasslands can be absent for many years. The next most extensive vegetation types are dwarf shrublands, dominated by Duosperma eremophilum on heavier, wetter sedimentary soils and Indigofera spinosa on stabilized dunes (White 1983). The shore of Lake Turkana is mostly rocky or sandy with little aquatic vegetation, and around the lake there are grassy plains on which yellow spear grass and doum palms (Hyphaene thebaica) predominate.
The ecoregion is moderately rich in species, but has a low level of endemism. Mt. Kulal and Mt. Marsabit both have some endemic plants, but these occur mainly at higher elevations, located in other ecoregions. The only strict endemic animals are aquatic: two species of toads (Bufo chappuisi, Bufo turkanae), a frog (Phrynobatrachus zavattarii), and a mud turtle (Pelusios broadleyi, VU) (Hilton-Taylor 2000). Four other species of reptile are regarded as near-endemic to the ecoregion. Lake Turkana has more than 350 species of aquatic and terrestrial birds, and is also an important flyway for migrant birds. Central Island has a breeding population of African skimmers (Rhyncops flavirostris) that nest in banks.
The grasses, shrubs and trees of the ecoregion are fire-tolerant because fires are frequent in the dry season. The arid-adapted mammalian fauna include Burchell's zebra (Equus burchelli), Grevy's zebra (Equus grevyi, EN), beisa oryx (Oryx beisa beisa, LR), Grant’s gazelle (Gazella granti), topi (Damaliscus lunatus), lion (Panthera leo), and cheetah (Acinonyx jubatus, VU) (Boitani 1999, East 1999). These species are all found in Sibiloi National Park and other areas within the ecoregion. Other mammals include leopard (Panthera pardus), reticulated giraffe (Giraffa camelpardalis reticulata), and elephant (Loxodonta africana). Among the small mammals there is also a near-endemic gerbil, Gerbillus pulvinatus.
Most habitats of this ecoregion have been considerably degraded by heavy grazing of domesticated livestock. Livestock populations as a result of veterinary programs and the supply of additional watering points. A comparatively small area of good quality habitat remains in the few protected areas: Sibiloi National Park on the northeastern edge of Lake Turkana, Mt. Kulal Biosphere Reserve extending north and east from the southeastern coast of Lake Turkana, and the Chew Bahr Wildlife Refuge in Ethiopia. Marsabit National Park is found in the central part of the ecoregion, but this mainly covers an isolated island of the habitat of the Northern Acacia-Commiphora Bushland and Thicket ecoregion. The habitats of the ecoregion are not particularly fragmented, but the populations of large wild mammals are greatly reduced. In particular, the black rhino (Diceros bicornis, CR) used to occur here, but has been exterminated through over-hunting.
Types and Severity of Threats
The main threats to natural resources are the rapid increases in both human and livestock populations which have caused widespread overgrazing and soil erosion, particularly in the north and have led to the threat of desertification. Lawlessness and poaching is rife along the Kenyan-Ethiopian border. Action is needed to combat these threats, particularly overgrazing and poaching, at the very least inside the protected areas.
Justification of Ecoregion Delineation
This ecoregion forms the southern outlier of White’s ‘Somalia-Masai semi-desert grassland and shrubland,’ including the area around Lake Turkana and the Chalbi Desert. Although, it contains a similar vegetation structure to the Ethiopian Xeric Grassland and Shrubland ecoregion further north, it was elevated to ecoregion status due to its disjunct position, arid nature, and elements of savanna woodland communities.
Boitani, L. 1999. A Databank for the Conservation and Management of the African Mammals. Instituto Ecologia Applicata, Rome, Italy.
East, R. (comp.) 1999. African Antelope Database 1998. IUCN/SSC Antelope Specialist Group. ICN, Gland, Switzerland and Cambridge, UK.
Hilton-Taylor, C. 2000. 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom.
White, F. 1983. The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000). UNESCO, Paris.
Prepared by: Chris Magin, Christine Burdette
Reviewed by: In progress